Multi-casing turbine

ABSTRACT

A multi-stage axial flow steam turbine having an inner and outer casing, the inner casing being a pressure vessel one end of which is open to the outer casing and the other end being closed by segmented nozzle chambers which are disposed around a rotor. A control stage and a plurality of reaction stages are disposed within the inner casing. The outer casing has a plurality of stages disposed therein so that steam leaving the inner casing flows over the outer peripheral surface of the inner casing and over the nozzle chambers, cooling them before entering the stages disposed in the outer casing. The inner casing is mounted within the outer casing in such a manner as to limit relative axial movement and allow free relative radial movement between the inner and outer casing, which is caused by changes in temperature. A steam pressure sealing device is provided between the nozzle chambers and the inner casing, the sealing device being adapted to allow free thermal expansion of the nozzle chamber with respect to the inner casing.

United States Patent [1 1 Stock et al.

MULTl-CASING TURBINE Inventors: Alvin L. Stock, Wallingford; Herman H. Wittig, Milmont Park; Louis Sangiorgio, Broomall, all of Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: July 26, 1971 Appl. No.: 166,221

US. Cl 415/136, 415/108, 415/219 R Int. Cl. F0ld 25/26, FOld 25/24 Field of Search 415/108, 179, 134,

[56] References Cited UNITED STATES PATENTS 4/1927 Hodgkinson 415/136 2,823,891 2/1958 Baker et al. 415/108 3,659,956 5/1972 Brinkman .1 415/108 FOREIGN PATENTS OR APPLICATIONS 661,822 11/1951 Great Britain 415/108 76,744 6/1919 Austria 415/136 1,126,806 7/1956 France.... 415/179 1,004,202 3/1957 Germany 415/108 [111 3,746,463 45] July 17, 1973 Primary Examiner1-lenry F. Raduazo Attorney-A. T. Stratton et al.

[57] ABSTRACT A multi-stage axial flow steam turbine having an inner and outer casing, the inner casing being a pressure vessel one end of which is open to the outer casing and the other end being closed by segmented nozzle chambers which are disposed around a rotor. A control stage and a plurality of reaction stages are disposed within the inner casing. The outer casing has a plurality of stages disposed therein so that steam leaving the inner casing flows over the outer peripheral surface of the inner casing and over the nozzle chambers, cooling them before entering the stages disposed in the outer casing. The inner casing is mounted within the outer casing in such a manner as to limit relative axial movement and allow free relative radial movement between the inner and outer casing, which is caused by changes in temperature. A steam pressure sealing device is provided between the nozzle chambers and the inner casing, the sealing device being adapted to allow free thermal expansion of the nozzle chamber with respect to the inner casing.

10 Claims, 4 Drawing Figures PA'IENIEWA 1 7191s SHEEI 3 UP 3 FIG.4

MULTI-CASING TURBINE BACKGROUND OF THE INVENTION This invention relates to multi-stage axial flow steam turbines, and more particularly to such turbines having an inner and outer casing.

One of the basic problems facing the turbine designer is introducing high pressure and high temperature steam into the main turbine casing and containing this steam before it is expanded through the blades of the turbine to do work. This process of expanding the steam produces work and reduces the temperature and pressure of the steam. Containment of the high temperature and pressure steam requires heavy wall containment vessels or casings having very large diameter bolts at horizontal joints as the casings are necessarily made in halves to provide easy access to the internals of the turbine and to facilitate assembly and maintenance. The high and varying temperature steam contained within the casing introduces thermal gradients across the thick walls of the casing. The thermal gradients produce differential thermal expansion across the thick walls causing thermal stresses, which produces plastic flow and distortion of the casing. These expansions and distortions must be considered by the designer, when setting the clearances between the rotating and stationary portions of the turbine. To reduce the thermal gradients across the thick walled casings, designers have built multi-casing turbines, breaking down the pressure and temperature gradients across the individual casings so that each casing, which is free to expand individually, is subjected to lower differential temperature and pressure and thus canbe made with thinner walls. The nozzle chambers have generally been disposed within the inner casing requiring a dimensionally large inner casing resulting in heavy walls, additional weight and cost. A further requirement when the nozzle chambers are placed within the inner casing is that a flexible slipjoint sleeve-type sealing arrangement be installed in the inlet steam piping between the outer casing and the nozzle chambers to allow movement between the outer casing and the nozzle as the temperature of the casings change during startup and load changes. These slip joint arrangements are expensive to manufacture and maintain.

SUMMARY OF THE INVENTION In general, an axial flow steam turbine made in accordance with this invention comprises in combination a rotor, an outer casing, a plurality of inlet nozzle chambers disposed within the outer casing, an inner casing disposed within the outer casing, keys and keyways for locating the inner casing axially with respect to the outer casing and allowing free radial movement of the inner casing with respect to the outer casing, an inlet conduit for each nozzle chamber, the inlet conduits extending through the outer casing, a flexible tubular expansion member adapted to form a seal between the outer casing and each inlet conduit, each nozzle chamher having a plurality of nozzles directing steam against an angular array of circumferentially spaced rotatable blades fastened to the rotor, the nozzle chambers being formed either continuously or in segments and disposed circumferentially around the rotor to provide an end closure for the inner casing, and a seal between said inner casing and said nozzle chambers. This seal is adapted to allow free expansion movement of the nozzl"e chambers with respect to the inner casing. The other end of the inner casing opens into the outer casing, and at least one stage of stationary and rotatable blades is disposed between the inner casing and the rotor downstream of the first mentioned rotatable blades. At least one stage of stationary and rotatable bladesis disposed between the outer casing and the r0- tor. The last mentioned blades are so. disposed that steam leaving the blades at the open end of the inner casing flows over the outer surface of the inner casing and the nozzle chambers, cooling the inner casing and nozzle chambers before entering; the last mentioned stage of stationary and rotatable blades.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIG. 1 shows a partial sectional view of an axial flow steam turbine 1 having an outer casing or cylinder 3, an inner casing or cylinder 5 and a rotor 7.

A plurality of inlet nozzle chambers 9 are disposed within the outer casing 3. The nozzle chambers 9 are formed in segments and are circumferentially disposed around the rotor 7. As shown in FIG. 4, abutting ends of the nozzle chambers 9 have a tongue and groove arrangement 10 providing an interlock, which allows radial movement of the nozzle chambers relatively to each other, but prevents relative axial movement. The tongue and groove arrangement 10 also provides seal between adjacent nozzle chambers. The nozzle chambers 9 provide an end closure for the inner casing 5. The nozzle chambers 9 each have a nozzle block 11, which contain a plurality of nozzles 13 for directing motive steam against an annular array of circumferentially spaced rotatable blades 15 fastened to the rotor 7 to form the first stage or control stage of the turbine- The inner casing 5 encircles the control stage and a plurality of rotating and stationary arrays of circumfcr entially spaced blades 17 forming a pair of reaction stages downstream of the control stage. The downstream end of the inner casing 5 opens into the outer casing 3.

As shown in FIG. 2, the inner casing 5 is a pressure vessel having a horizontal joint in a plane extending through the axis of the rotor to divide the innercasing into upper and lower halves 21 and 23, respectively. Bolts 25 fasten the inner casing havles together to form a vessel.

The inner casing 5 is mounted within the outer casing 3 by a plurality of keys and keyways 27, fitted pins 28, and axial alignment fits is obtained by tongue and groove portions 29 which locate the inner casing 5 axially with respect to the outer casing and yet allow free radial movement of the inner casing with respect to the outer casing, thus providing for differential thermal expansion of the casings as the turbine is brought up to load and during load changes.

As shown in FIG. 3 the nozzle chamber 9 and inner casing 5 are so disposed that the nozzle chamber forms an end closure for the inner casing 5 and a seal 30 is disposed between the inner casing 5 and a circumferential flange portion extending from the nozzle chamber 9 and around the inner casing 5. The seal 30 is a labyrinth seal formed from a seal ring 31 made from a plurality of segments encircling the inner casing. The segments are mounted in a T-shaped groove 32 and biased outwardly by a plurality of leaf springs 33. The nozzle blocks 11 have a plurality of raised circumferential rings 35 which interdigitate with circumferential fins 37 to allow free movement of the nozzle blocks 11 with respect to the inner casing 5. A plurality of labyrinth seals 39, 40 and 41 are disposed on the nozzle blocks and the nozzle chambers adjacent the rotor, to seal the one end of the inner casing and allow free movement of the nozzle blocks relative to the inner cylinder. While only a single embodiment is shown, there are several sealing arrangements which could be utilized to form the seal between the nozzle chambers and the inner casing.

As shown in FIG. 1, an inlet conduit 43 for each inlet nozzle chamber 9 extends through the outer casing 3 and a flexible tubular expansion member 45 is welded to the inlet conduit 43 and to the outer casing 3 forming a seal and a semirigid connection between the outer casing 3 and the nozzle chambers 9, thus eliminating the expensive slip-joint seal utilized to provide differential expansion between the nozzle chambers and the outer casing when the nozzle chambers 9 are fastened directly to the inner casing 5.

One end of the inner casing 5 is open to the outer casing 3 and a plurality of annular arrays of circumferentially spaced stationary and rotatable blades 47 are disposed between the outer casing and the rotor to provide a plurality of reaction stages on the closed side of the inner casing 5 so that steam leaving the inner casing passes over the outer peripheral surface of the inner casing 5 and over the outside of the nozzle chamber 9 cooling these portions of the turbine before entering the downstream stages of the turbine. Cooling the inner casing 5 and nozzle chambers 9 reduces the temperature and increases-the allowable unit stress, thus allowing thinner walled structures, which are more economical to manufacture and handle in the field.

Reducing the temperature and pressure of the steam before it leaves the inner casing by providing a plurality of reaction stages within the inner casing 5 reduces the temperature and pressure to which the outer casing 3 is subjected and thus, increases the allowable unit stress and reduces the stress due to the smaller pressure differential across the outer casing so that the outer casing can be made much thinner reducing the manufacturing cost, and making the turbine smaller and easier to assemble and disassemble in the field.

What is claimed is:

I. An axial flow steam turbine comprising in combination I a rotor an outer casing,

a plurality of inlet nozzle chambers disposed within the outer casing,

\ an inner casing disposed within the outer casing,

mounting means for locating the inner casing axially with respect to the outer casing and allowing free radial movement of the inner casing with respect to the outer casing,

said mounting means comprising a pair of diametrically opposed tongue and groove portions and a pin extending radially through said tongue and groove portions,

an inlet conduit for each inlet nozzle chamber, the inlet conduits extending through the outer casing,

a flexible tubular expansion member adapted to form a'seal between the outer casing and each inlet conduit,

each nozzle chamber having a plurality of nozzles for directing steam against an annular array of circumferentially spaced rotatable blades fastened to the rotor,

the nozzle chambers being formed in segments and disposed circumferentially around the rotor to provide an end closure for one end of the inner casing,

a seal between said inner casing and said nozzle chambers, said seal being adapted to allow free movement of said nozzle chambers with respect to said inner casing,

the other end of said inner casing opening into said outer casing,

at least one stage of stationary and rotatable blades disposed between said inner casing and said rotor downstream of said first mentioned rotatable blades,

at least one stage of stationary and rotatable blades disposed between said outer casing and said rotor, said last mentioned blades being so disposed that steam leaving said open end of said inner casing flows over the outer surface of said inner casing and over said nozzle chambers cooling said inner casing and nozzle chambers before entering said last mentioned stage of stationary and rotatable blades.

2. A turbine as set forth in claim 1, wherein abutting ends of the segmented nozzle chambers interlock to form an annular array of nozzle chambers.

3. A turbine as set forth in claim 2, wherein the interlock is such that the nozzle chambers are free to move in any direction relative to each other except axial.

4. A turbine as set forth in claim 1 and further comprises a seal between the nozzle chambers and the rotor.

5. A turbine as set forth in claim 1, wherein the inner and outer casings have a horizontal joint in a plane through the axis of the rotor.

6. A turbine as set forth in claim I, wherein a plurality of stages of rotatable and stationary blades are disposed between the inner casing and the rotor downstream of the first mentioned rotatable blades.

7. A turbine as set forth in claim 1, wherein the inlet conduits are welded to the tubular members and the tubular members are welded to the outer casing.

8. A turbine as set forth in claim 1, wherein the inner casing, nozzle chambers and seal cooperate to provide a pressure vessel disposed within the outer casing.

9. A turbine as set forth in claim 1, wherein the mounting means further comprises a pair of diametrically opposed keys and keyways which cooperate with the tongue and groove portions to locate the inner casing axially and allow free radial movement of the inner v casing with respect to the outer casing.

10. An axial flow steam turbine comprising in combination a rotor an outer casing,

a plurality of inlet nozzle chambers disposed within the outer casing,

an inner casing disposed within the outer casing,

mounting means for locating the inner casing axially with respect to the outer casing and allowing free radial movement of the inner casing with respect to the outer casing,

an inlet conduit for each inlet nozzle chamber, the inlet conduits extending through the outer casing,

a flexible tubular expansion member adapted to form a seal between the outer casing and each inlet conduit,

each nozzle chamber having a plurality of nozzles for directing steam against an annular array of circumferentially spaced rotatable blades fastened to the rotor,

the nozzle chambers being formed in segments and disposed circumferentially around the rotor to provide an end closure for one end of the inner casing,

a seal between said inner casing and said nozzle chambers, said seal being adapted to allow free movement of said nozzle chambers with respect to said inner casing,

each nozzle segment having a circumferentially extending flange portion extending over said inner casing, said seal being disposed between said flange portion and said inner casing,

the other end of said inner'casing opening into said outer casing,

at least one stage of stationary and rotatable blades disposed between said inner casing and said rotor downstream of said first mentioned rotatable blades,

at least one stage of stationary and rotatable blades disposed between said outer casing and said rotor, said last mentioned blades being so disposed that steam leaving said open end of said inner casing flows over the outer surface of said inner casing and over said nozzle chambers cooling said inner casing and nozzle chambers before entering said last mentioned stage of stationary and rotatable blades. 

1. An axial flow steam turbine comprising in combination a rotor an outer casing, a plurality of inlet nozzle chambers disposed within the outer casing, an inner casing disposed within the outer casing, mounting means for locating the inner casing axially with respect to the outer casing and allowing free radial movement of the inner casing with respect to the outer casing, said mounting means comprising a pair of diametrically opposed tongue and groove portions and a pin extending radiAlly through said tongue and groove portions, an inlet conduit for each inlet nozzle chamber, the inlet conduits extending through the outer casing, a flexible tubular expansion member adapted to form a seal between the outer casing and each inlet conduit, each nozzle chamber having a plurality of nozzles for directing steam against an annular array of circumferentially spaced rotatable blades fastened to the rotor, the nozzle chambers being formed in segments and disposed circumferentially around the rotor to provide an end closure for one end of the inner casing, a seal between said inner casing and said nozzle chambers, said seal being adapted to allow free movement of said nozzle chambers with respect to said inner casing, the other end of said inner casing opening into said outer casing, at least one stage of stationary and rotatable blades disposed between said inner casing and said rotor downstream of said first mentioned rotatable blades, at least one stage of stationary and rotatable blades disposed between said outer casing and said rotor, said last mentioned blades being so disposed that steam leaving said open end of said inner casing flows over the outer surface of said inner casing and over said nozzle chambers cooling said inner casing and nozzle chambers before entering said last mentioned stage of stationary and rotatable blades.
 2. A turbine as set forth in claim 1, wherein abutting ends of the segmented nozzle chambers interlock to form an annular array of nozzle chambers.
 3. A turbine as set forth in claim 2, wherein the interlock is such that the nozzle chambers are free to move in any direction relative to each other except axial.
 4. A turbine as set forth in claim 1 and further comprises a seal between the nozzle chambers and the rotor.
 5. A turbine as set forth in claim 1, wherein the inner and outer casings have a horizontal joint in a plane through the axis of the rotor.
 6. A turbine as set forth in claim 1, wherein a plurality of stages of rotatable and stationary blades are disposed between the inner casing and the rotor downstream of the first mentioned rotatable blades.
 7. A turbine as set forth in claim 1, wherein the inlet conduits are welded to the tubular members and the tubular members are welded to the outer casing.
 8. A turbine as set forth in claim 1, wherein the inner casing, nozzle chambers and seal cooperate to provide a pressure vessel disposed within the outer casing.
 9. A turbine as set forth in claim 1, wherein the mounting means further comprises a pair of diametrically opposed keys and keyways which cooperate with the tongue and groove portions to locate the inner casing axially and allow free radial movement of the inner casing with respect to the outer casing.
 10. An axial flow steam turbine comprising in combination a rotor an outer casing, a plurality of inlet nozzle chambers disposed within the outer casing, an inner casing disposed within the outer casing, mounting means for locating the inner casing axially with respect to the outer casing and allowing free radial movement of the inner casing with respect to the outer casing, an inlet conduit for each inlet nozzle chamber, the inlet conduits extending through the outer casing, a flexible tubular expansion member adapted to form a seal between the outer casing and each inlet conduit, each nozzle chamber having a plurality of nozzles for directing steam against an annular array of circumferentially spaced rotatable blades fastened to the rotor, the nozzle chambers being formed in segments and disposed circumferentially around the rotor to provide an end closure for one end of the inner casing, a seal between said inner casing and said nozzle chambers, said seal being adapted to allow free movement of said nozzle chambers with respect to said inner casing, each nozzle segment having a circumferentially extending flange portion extending over said inner casing, saId seal being disposed between said flange portion and said inner casing, the other end of said inner casing opening into said outer casing, at least one stage of stationary and rotatable blades disposed between said inner casing and said rotor downstream of said first mentioned rotatable blades, at least one stage of stationary and rotatable blades disposed between said outer casing and said rotor, said last mentioned blades being so disposed that steam leaving said open end of said inner casing flows over the outer surface of said inner casing and over said nozzle chambers cooling said inner casing and nozzle chambers before entering said last mentioned stage of stationary and rotatable blades. 